This invention relates to a piston and cylinder assembly, wherein the piston partially defines a fluid chamber in the cylinder from which fluid is expelled through an outlet port of the cylinder by movement of the piston along the cylinder. The invention also includes a flow restrictor device for use in such a piston and cylinder arrangement.
It is known in such an assembly to provide a flow restrictor device in the form of a snubbing ring carried by the piston and having an axially extending groove in its outer peripheral surface communicating with the port. As the piston moves past the port during operation of the assembly, the ring partially seals the port and the ring groove provides restricted communication between the chamber and port, permitting the piston to be decelerated in a controlled manner towards the end of its operative stroke.
The invention provides a piston and cylinder assembly, wherein the piston partially defines a fluid chamber in the cylinder from which fluid is expelled through an outlet port of the cylinder by movement of the piston along the cylinder, the assembly including flow restrictor means providing a first restricted flow path between the chamber and port, said means also providing an auxiliary restricted flow path of which a first portion communicates with the chamber and of which a second portion extends between the first portion and the port.
Such an arrangement provides alternative controlled release routes for fluid from the chamber through the port, ensuring continued controlled deceleration of the piston in the event that a blockage occurs in one of the flow paths.
Preferably, the first portion of the auxiliary flow path is circumferentially spaced from the first flow path and conveniently extends axially, the second portion of the auxiliary flow path conveniently extending circumferentially.
In one convenient arrangement, the second portion of the auxiliary flow path includes a portion of the first restricted flow path spaced from the chamber axially along the cylinder.
The flow paths may be passageways formed in the piston and are conveniently of uniform cross-sectional dimension. The passageways are, typically, in the form of grooves in the outer periphery of the piston.
Alternatively, the passageways may be formed in a ring carried by the piston or cylinder, the flow paths then conveniently being grooves formed in the ring.
The invention also includes a restrictor device in the form of a ring for mounting in a piston and cylinder assembly, the ring having a plurality of axially extending passageways interconnected by a further passageway, which may conveniently extend circumferentially, for providing alternative restricted routes for releasing fluid into a port from a chamber partially defined by the piston.
Conveniently, the ring is mountable on the piston, the channels typically being formed by grooves in the outer periphery of the ring.